Overview

We are currently working to understand the factors that make better supported nanoparticle catalysts. We want to understand how or why one catalyst is more or less active than another. In simple terms, there are two ways that two catalysts can have different activities: (1) A catalyst can have a greater number of active sites, possibly by having smaller nanoparticles or having a greater number of the specific atomic arrangements, interactions, or co-catalysts that make up the catalytic active site for a particular reaction. (2) A catalyst might have inherently more active sites, perhaps through electronic interactions with a support or by incorporating additional metals in the catalyst formulation. Measuring and differentiating between these two possibilities is important to us, along with understanding catalytic reaction mechanisms and preparing new catalytic materials.

Research Areas and Projects

Gold Catalyzed CO Oxidation

CO oxidation over small (2-5 nm) Au nanoparticles has generated a tremendous amount of interest since it's discovery about 1990. In spite of the wide interest and extensive number of publications on the subject, the reaction mechanism and the role of the support is not particularly well understood. We are currently performing a mechanistic study to help unravel the mechanistic details of the reaction. This includes employing a Michaelis-Menten treatmnt (pub 15) that allows us to distinguish between changes in the number of active sites from changes in inherent reactivity. Our most recent work (pub 25) described the role that surface carbonates play in affecting catalyst activity. Current Students: Dr. Johnny Saavedra, Adhwaith ManiPast Students: R. Alan May, Anil Singh, Bethany Auten, Dr. Cormac Long

Developing Kinetic Probes to Understand & Characterize Catalysts.

Reaction kinetics are the original in-situ catalyst characterization technique, and understanding catalytic mechanisms requires careful kinetic mechanisms. We are adapting and applying traditional physical organic chemistry and even biochemistry techniques to the study of heterogeneous catalysts. Beyond improving our understanding of reaction mechanisms, traditional mechanistic chemistry tools are well understood and based on sound chemical principles. This means that they offer offer unique opportunities to probe subtle differences in transition states. Since the key transition states are often closely tied to changes in the catalyst in a catalytic reaction, this offers opportunities to use kinetics as a catalyst characterization tool. Our initial efforts used Michaelis-Menten approaches to quantify differences between catalysts (pubs 15, 20, 23, & 25). Our most recent effort (pub 25) extended this to intentional poisoning experiments (see figure from pub 23), which suggested that only corner and edge atoms (or a subset of them) are involved in CO oxidation catalysis. This continues to be a major theme for us, and additional studies and techniques should be published shortly.

Most of this work has involved CO adsorption on Au catalysts, and was performed in Dr. Chris Pursell's lab. We have examined CO adsorption isotherms on Au catalysts and developed a Temkin adsorption model for this system (pubs 19, 22, and 24). As we examine more catalysts, we are evaluating the Temkin adsorption metrics as characterization data for Au catalysts, and trying to understand the underlying electronic factors that affect CO adsorption. We are beginning to look at the adsorption of a variety of other small molecules using infrared spectroscopy and a variety of complementary techniques.